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<div class="moz-cite-prefix">On 3/26/24 3:10 PM, Gautam Menghani
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20240326094035.115835-1-gautam@linux.ibm.com">
<pre class="moz-quote-pre" wrap="">PAPR hypervisor has introduced three new counters in the VPA area of
LPAR CPUs for KVM L2 guest (see [1] for terminology) observability - 2
for context switches from host to guest and vice versa, and 1 counter
for getting the total time spent inside the KVM guest. Add a tracepoint
that enables reading the counters for use by ftrace/perf. Note that this
tracepoint is only available for nestedv2 API (i.e, KVM on PowerVM).
Also maintain an aggregation of the context switch times in vcpu->arch.
This will be useful in getting the aggregate times with a pmu driver
which will be upstreamed in the near future.
[1] Terminology:
a. L1 refers to the VM (LPAR) booted on top of PAPR hypervisor
b. L2 refers to the KVM guest booted on top of L1.
Signed-off-by: Vaibhav Jain <a class="moz-txt-link-rfc2396E" href="mailto:vaibhav@linux.ibm.com"><vaibhav@linux.ibm.com></a>
Signed-off-by: Gautam Menghani <a class="moz-txt-link-rfc2396E" href="mailto:gautam@linux.ibm.com"><gautam@linux.ibm.com></a>
---
v1 -> v2:
1. Fix the build error due to invalid struct member reference.
v2 -> v3:
1. Move the counter disabling and zeroing code to a different function.
2. Move the get_lppaca() inside the tracepoint_enabled() branch.
3. Add the aggregation logic to maintain total context switch time.
v3 -> v4:
1. After vcpu_run, check the VPA flag instead of checking for tracepoint
being enabled for disabling the cs time accumulation.
arch/powerpc/include/asm/kvm_host.h | 5 +++++
arch/powerpc/include/asm/lppaca.h | 11 ++++++++---
arch/powerpc/kvm/book3s_hv.c | 30 +++++++++++++++++++++++++++++
arch/powerpc/kvm/trace_hv.h | 25 ++++++++++++++++++++++++
4 files changed, 68 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 8abac5321..d953b32dd 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -847,6 +847,11 @@ struct kvm_vcpu_arch {
gpa_t nested_io_gpr;
/* For nested APIv2 guests*/
struct kvmhv_nestedv2_io nestedv2_io;
+
+ /* Aggregate context switch and guest run time info (in ns) */
+ u64 l1_to_l2_cs_agg;
+ u64 l2_to_l1_cs_agg;
+ u64 l2_runtime_agg;
#endif
#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h
index 61ec2447d..bda6b86b9 100644
--- a/arch/powerpc/include/asm/lppaca.h
+++ b/arch/powerpc/include/asm/lppaca.h
@@ -62,7 +62,8 @@ struct lppaca {
u8 donate_dedicated_cpu; /* Donate dedicated CPU cycles */
u8 fpregs_in_use;
u8 pmcregs_in_use;
- u8 reserved8[28];
+ u8 l2_accumul_cntrs_enable; /* Enable usage of counters for KVM guest */
+ u8 reserved8[27];
__be64 wait_state_cycles; /* Wait cycles for this proc */
u8 reserved9[28];
__be16 slb_count; /* # of SLBs to maintain */
@@ -92,9 +93,13 @@ struct lppaca {
/* cacheline 4-5 */
__be32 page_ins; /* CMO Hint - # page ins by OS */
- u8 reserved12[148];
+ u8 reserved12[28];
+ volatile __be64 l1_to_l2_cs_tb;
+ volatile __be64 l2_to_l1_cs_tb;
+ volatile __be64 l2_runtime_tb;
+ u8 reserved13[96];
volatile __be64 dtl_idx; /* Dispatch Trace Log head index */
- u8 reserved13[96];
+ u8 reserved14[96];
} ____cacheline_aligned;
#define lppaca_of(cpu) (*paca_ptrs[cpu]->lppaca_ptr)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 8e86eb577..dcd6edd3b 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4108,6 +4108,27 @@ static void vcpu_vpa_increment_dispatch(struct kvm_vcpu *vcpu)
}
}
+static void do_trace_nested_cs_time(struct kvm_vcpu *vcpu)
+{
+ struct lppaca *lp = get_lppaca();
+ u64 l1_to_l2_ns, l2_to_l1_ns, l2_runtime_ns;
+
+ l1_to_l2_ns = tb_to_ns(be64_to_cpu(lp->l1_to_l2_cs_tb));
+ l2_to_l1_ns = tb_to_ns(be64_to_cpu(lp->l2_to_l1_cs_tb));
+ l2_runtime_ns = tb_to_ns(be64_to_cpu(lp->l2_runtime_tb));
+ trace_kvmppc_vcpu_exit_cs_time(vcpu, l1_to_l2_ns, l2_to_l1_ns,
+ l2_runtime_ns);
+ lp->l1_to_l2_cs_tb = 0;
+ lp->l2_to_l1_cs_tb = 0;
+ lp->l2_runtime_tb = 0;
+ lp->l2_accumul_cntrs_enable = 0;
+
+ // Maintain an aggregate of context switch times
+ vcpu->arch.l1_to_l2_cs_agg += l1_to_l2_ns;
+ vcpu->arch.l2_to_l1_cs_agg += l2_to_l1_ns;
+ vcpu->arch.l2_runtime_agg += l2_runtime_ns;
+}
+
static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
unsigned long lpcr, u64 *tb)
{
@@ -4130,6 +4151,11 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
kvmppc_gse_put_u64(io->vcpu_run_input, KVMPPC_GSID_LPCR, lpcr);
accumulate_time(vcpu, &vcpu->arch.in_guest);
+
+ /* Enable the guest host context switch time tracking */
+ if (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled()))
+ get_lppaca()->l2_accumul_cntrs_enable = 1;</pre>
</blockquote>
<br>
<font face="monospace">can we wrap "<span
style="white-space: pre-wrap">get_lppaca()->l2_accumul_cntrs_enable" under wrapper function</span>
</font><br>
<font face="monospace">like is_<span style="white-space: pre-wrap">l2_accumul_cntrs_enable(), set_</span><span
style="white-space: pre-wrap">l2_accumul_cntrs_enable() and </span></font><br>
<font face="monospace"><span style="white-space: pre-wrap">unset_</span><span
style="white-space: pre-wrap">l2_accumul_cntrs_enable()?</span></font><br>
<br>
<font face="monospace"><span style="white-space: pre-wrap">set/unset does not need a parameter and </span><span
style="white-space: pre-wrap">in future incase if we want to</span><br>
<span style="white-space: pre-wrap">check and set or check and unset, we could have additional code in there.</span></font>
<p><span style="white-space: pre-wrap"><font face="monospace">Maddy</font></span></p>
<p><span style="white-space: pre-wrap"></span></p>
<p><span style="white-space: pre-wrap"></span></p>
<p><span style="white-space: pre-wrap">
</span></p>
<blockquote type="cite"
cite="mid:20240326094035.115835-1-gautam@linux.ibm.com">
<pre class="moz-quote-pre" wrap="">
+
rc = plpar_guest_run_vcpu(0, vcpu->kvm->arch.lpid, vcpu->vcpu_id,
&trap, &i);
@@ -4156,6 +4182,10 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
timer_rearm_host_dec(*tb);
+ /* Record context switch and guest_run_time data */
+ if (get_lppaca()->l2_accumul_cntrs_enable)
+ do_trace_nested_cs_time(vcpu);
+
return trap;
}
diff --git a/arch/powerpc/kvm/trace_hv.h b/arch/powerpc/kvm/trace_hv.h
index 8d57c8428..ab19977c9 100644
--- a/arch/powerpc/kvm/trace_hv.h
+++ b/arch/powerpc/kvm/trace_hv.h
@@ -491,6 +491,31 @@ TRACE_EVENT(kvmppc_run_vcpu_enter,
TP_printk("VCPU %d: tgid=%d", __entry->vcpu_id, __entry->tgid)
);
+TRACE_EVENT(kvmppc_vcpu_exit_cs_time,
+ TP_PROTO(struct kvm_vcpu *vcpu, u64 l1_to_l2_cs, u64 l2_to_l1_cs,
+ u64 l2_runtime),
+
+ TP_ARGS(vcpu, l1_to_l2_cs, l2_to_l1_cs, l2_runtime),
+
+ TP_STRUCT__entry(
+ __field(int, vcpu_id)
+ __field(__u64, l1_to_l2_cs_ns)
+ __field(__u64, l2_to_l1_cs_ns)
+ __field(__u64, l2_runtime_ns)
+ ),
+
+ TP_fast_assign(
+ __entry->vcpu_id = vcpu->vcpu_id;
+ __entry->l1_to_l2_cs_ns = l1_to_l2_cs;
+ __entry->l2_to_l1_cs_ns = l2_to_l1_cs;
+ __entry->l2_runtime_ns = l2_runtime;
+ ),
+
+ TP_printk("VCPU %d: l1_to_l2_cs_time=%llu-ns l2_to_l1_cs_time=%llu-ns l2_runtime=%llu-ns",
+ __entry->vcpu_id, __entry->l1_to_l2_cs_ns,
+ __entry->l2_to_l1_cs_ns, __entry->l2_runtime_ns)
+);
+
TRACE_EVENT(kvmppc_run_vcpu_exit,
TP_PROTO(struct kvm_vcpu *vcpu),
</pre>
</blockquote>
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